This invention relates generally to air conditioning systems and, more particularly, to an air conditioning system for the rooftop of a bus.
The most common approach for air conditioning a bus is to locate the air conditioning components on the rooftop thereof Inasmuch as power is available from the engine that drives the bus, it has become common practice to locate the air conditioning compressor near the drive engine such that the drive engine is drivingly connected to the compressor, with the compressor then being fluidly interconnected to the air conditioning system on a rooftop of a bus. This, of course, requires rather extensive piping between the engine compartment and the air conditioning unit, thereby increasing installation and maintenance costs.
Another problem with such existing systems is that the speed that the compressor is driven is dependent on the speed in which the drive engine is running. Thus, when the drive engine is idling in a parking lot, for example, the compressor is running at a relatively slow speed which may not be sufficient to provide the desired degree of air conditioning. It is therefore generally necessary to oversize the compressor in order to obtain the performance needed under these conditions.
Others problems associated with such a motor driven compressor system is that the open drive compressor needs a shaft seal and a mechanical clutch, both of which are subject to maintenance problems. Further, since DC power is available on a bus, DC motors have been used for the air conditioning system In general, DC motors are not as reliable as AC motors since they have brushes that wear out, and brushless motors are relatively expensive.
In addition to the problems discussed hereinabove, it is recognized, that because the wide variety of bus types and application requirements, it has been necessary to provide many different types and variations of air conditioning systems in order to meet these different requirements and vehicle interfaces. As a result, the manufacturing and installation costs, and sustaining engineering resources that are necessary in order to properly maintain and service these units, are relatively high.
Also associated with the existing bus air conditioning systems is the problem of a component failure causing a complete loss of the air conditioning capacity. That is, with a single large unit as is now customary, failure of that unit such as, for example, a leaking hose causing loss of refrigerant, an electrical failure leading to inoperation of one of the components such as a fan, or a compressor failure, the entire unit is inoperable and no air conditioning can be provided to the unit. In such a situation, it would preferable if partial capacity could be maintained in order to provide a “limp home” capability.
In addition to the function of cooling the air in a passenger compartment of a bus, it is also necessary to warm the air when the ambient conditions are cold Again, it is common to use the energy that is available at the drive engine, with the heat coming from the engine coolant. But, similar to the case of cooling, less heat will be available when the engine is idling, for example.
Generally speaking, the capacity of a compressor is typically proportional to the diameter of the compressor. Similarly, the cost effectiveness of a compressor is related to the aspect ratio of the compressor, thus from am cost effectiveness standpoint, it is undesirable to have long skinny compressors. Therefore, typical hermitic, high volume and low cost compressors are only manufactured in discrete aspect ratios.
A proposed approach, involves locating the air conditioning system for a bus on the roof of the bus. Locating the air conditioning system to the roof of the bus requires that, when installed, the air conditioning system does not cause the height of the bus to exceed operational limits that would cause the bus to strike overhead objects, such as, for example, signs, bridges and overpasses when passing underneath. In addition, bus manufacturers prefer for styling and aesthetic reasons that the air conditioning units protrude above the roofline as little as possible. Likewise, for a cost effective system, the aspect ratio of the compressor must fall within a certain range. For example, for a given diameter and compressor efficiency, the length of the compressor typically will fall within a small range of lengths.
It is therefore an object of the present invention to provide an improved bus top air conditioning system
Another object of the present invention is the provision for a bus air conditioning system which is effective at all operating speeds of the bus, while at the same time does not require an oversized compressor.
Yet another object of the present invention is the provision for reducing the manufacturing, installation, and maintenance costs of a bus air conditioning system.
Still another object of the present invention is that of providing an air conditioning system that is designed for adaptability of use in various types of installation configurations.
Another object of the present invention is that of providing a “limp home” capability in the event of certain component failures.
Still another object of the present invention is the provision in a rooftop air conditioning system for effectively providing heat to the passenger compartment, regardless of engine speed.
Yet another object of the present invention is the provision for a bus rooftop air conditioning system which is economical to manufacture and effective in use.
Yet another object of the present invention is the provision of a low profile rooftop air conditioning system.
Yet another object of the present invention is the provision of an aesthetically pleasing rooftop air conditioning system.
Yet another object of the present invention is the provision of a lower drag rooftop air conditioning system.
These objects and other features and advantages become more readily apparent upon reference to the following descriptions when taken in conjunction with the appended drawings.